We have made the previous unpublished observation that a protein, estrogen-stimulated neurophysin (ESN), known to be a carrier of oxytocin was elevated in a group of essential hypertensives. This screening was extended to a larger group of essential hypertensives and again 23% of the population had elevation of ESN. Since ESN has no intrinsic activity but its presence in plasma is a reflection of secretion of oxytocin, we would like to initiate a preliminary study to determine the level of oxytocin in plasma of essential hypertensives. We plan to maintain patients on low and high sodium diets while monitoring blood pressure in hopes to identify a salt sensitive sub-group of hypertensives. It is in this group that we expect to find a positive correlation between salt sensitivity and high levels of oxytocin in plasma, this derives from previous work on oxytocin involvement in salt and water retention. It this preliminary study is fruitful, we would hope to extend investigation to elucidate the mechanism whereby oxytocin is involved in development of hypertension.